Floor box (1) comprising an electric insert (42) placed in a connection cavity (41) in the floor box (1), fastening devices (4) to fasten the floor box (1) in a floor (22), a radially directed circular abutment flange (2) as well as a circularly shaped lid (3) placed above a circular opening (54) in the floor box (1) to cover the connection cavity (41) of the floor box (1), the abutment flange (2) transforming into the circular opening (54) that is formed with a cylindrical wall (55) having an inner surface (57) integrally with the abutment flange (2), which wall (55) transforms into an integral, radially orientated bottom surface (56) against which bottom surface (56) the lid abuts, an O-ring seal (45) being placed in a seal groove (53) in and around the periphery of the lid (3) so that the seal (45) abuts against the cylindrical wall (55) when the lid (3) is applied.